1. Field of the Invention
The present invention relates to a method of measuring surface properties within small areas on substrates, and more particularly a method of using an ellipsometer to measure within small pads on semiconductor wafers.
2. Description of Related Art
Spectroscopic ellipsometers are well-known metrology tools useful in a variety of scientific or technological fields, for example, biology, geology, forensics, nutrition science, medicine, and semiconductor processing, as well as manufacturing of flat panel displays and read/write and glide heads. Spectroscopic ellipsometers are instruments that measure the alteration of the polarization of light that is reflected from a sample. Ellipsometers typically reflect a known polarization state of polarized light at an oblique angle off the sample and detect any changes to the polarization state of the light. Changes in the polarization state of the light can be used to determine specific properties of the sample or films on the sample.
In one application, ellipsometers are used to accurately and precisely measure the properties of thin films on flat substrates, such as wafers or flat panel displays. Most commonly, ellipsometers are used as “stand-alone” metrology tools such as that disclosed in U.S. Pat. No. 5,596,406.
Spectroscopic ellipsometers gather more information, and thus provide better measurements, than single wavelength ellipsometers. However, spectroscopic ellipsometers have larger spot sizes, which limits their ability to measure within small areas. Moreover in the semiconductor industry, there continues to be a drive to miniaturize components of integrated circuits. In addition to other problems, miniaturization requires the measurement of surface characteristics within increasingly smaller areas. Thus, what is needed is a cost-effective method of measuring within small areas on substrates using an ellipsometer.